Photofinishers that use photosensitive paper to produce color prints desire short processing times in order to increase output. One way of obtaining rapid processing times is to accelerate the development time by increasing the chloride content of the emulsions used in the photographic paper. However, increasing chloride content has attendant disadvantages, one of which is the increased propensity for storage deterioration.
Photographic emulsions that have high silver chloride content are prone to fogging and sensitivity changes when stored in high temperature and humidity conditions. Such changes may vary from layer to layer thus resulting in color imbalance and loss of quality in the printed material. Attempts have been made to reduce fog formation during storage by addition of inhibitory agents to the silver halide emulsions. For example, U.S. Pat. Nos. 2,440,110; 3,043,696; 3,057,725; 3,226,232; 3,397,986; 3,447,925; and 3,761,277, as well as Defensive Publication 864,011, describe the addition of organic disulfides to silver halide emulsions to lessen the tendency towards fog growth.
High chloride photographic emulsions also have an undesirable sensitivity to temperature changes during printing. For example, when the temperature of an emulsion upon printing increases due to a rise in room temperature, temperature irregularities of the printer's platen, or heat from an exposing element, the print density changes if the printing conditions are left at the initial set values. This may result in prints whose densities are different from those exposed at the normal temperature. This density difference contributes to print variability and is not acceptable to photofinishers. Very often, an increase in temperature during printing of the paper may result in a selective increase in speed in one layer, for instance the cyan layer, over another light sensitive layer, such as the magenta layer. This results in improper color balance of the color print, and requires the photofinisher to readjust printing conditions in order to compensate for the density fluctuation. Operating efficiency thus suffers.
The deficiencies of using high silver chloride emulsions is recognized in the art. In particular, EP 0 367 227 (1988) discusses reducing heat sensitivity by employing certain spectral sensitizing dyes in combination with mercapto azoles. However, these dye structures have not proved to be entirely satisfactory in terms of minimizing heat sensitivity while still maintaining optimal sensitization efficiency. EP 0 325 235 describes using iron ion donating compounds in high chloride photographic elements to reduce their change in sensitivity due to exposure at elevated temperatures. A combination of sulfinate and diamino disulfides has been used to address this problem in U.S. Pat. No. 5,356,770. Despite these attempts to address the heat sensitivity problem, no solution has been found which completely eliminates the above concerns.
U.S. Statutory Invention Registration H706 and EP 0 305 926 disclose the use of sulfinates in combination with sulfonates to reduce stain in photographic paper. U.S. Pat. No. 2,440,206 discloses the use of the combination of sulfinates and small amounts of polythionic acids to stabilize photographic emulsions against fog growth. U.S. Pat. No. 2,440,110 discloses the combination sulfinates and small amounts of aromatic or heterocyclic polysulfides as being effective in controlling fog growth. EP 0 358 170 discloses the combination of thiosulfonates and sulfinates for sensitization of direct positive photographic materials. In EP 0 267 483, sulfinates are added during the sensitization of silver bromide emulsions. The use of a paper base which has been treated with a sulfinic acid salt is known from U.S. Pat. No. 4,410,619. Similarly, British Patent 1,308,938 discloses the use of sulfinates during processing to minimize discoloration of the image tone. Sulfinates are also described as having fog reducing properties in U.S. Pat, No. 2,057,764.
Two references, U.S. Pat. Nos. 4,115,129 and 5,266,457, disclose the incorporation of phosphorous containing compounds in photographic emulsions and elements. In U.S. Pat. No. 5,266,457, sulfur sensitizers containing a thiophosphoryl moiety are disclosed as being stable under varying pH and pAg conditions. The photographic materials described in this patent are also alleged to exhibit improved antifogging, reproducibility, and sensitivity. In U.S. Pat. No. 4,115,129, photographic silver halide emulsions sensitized by digestion at a pH of at least 7 with an organophosphine sulfide added before or during digestion are disclosed. Neither patent, however, provides a means by which to adequately control the sensitivity response of high chloride emulsions to changing temperatures during printing. Thus, there remains the need for the development of effective methods for controlling the heat sensitivity of photographic emulsions and elements. Further, there exists the desire to provide such methods that will also be capable of enhancing the storage stability of photographic emulsions and elements.